The present invention relates to sealed insulating units, especially but not exclusively sealed double glazing units, and, in particular, to a form of construction of sealing insulating units which provides an assured long lifetime, to a method of constructing sealed insulating units to achieve an assured long lifetime, and to the use of a thick primary seal to achieve such a lifetime. The present invention also relates to spacer frame constructions for such units.
In a well known form of construction, a sealed double glazing unit comprises two parallel opposed panes of transparent or translucent glazing material, usually but not necessarily glass, with a spacing and sealing system therebetween defining, with the panes, a sealed gas space. The space usually contains air, but selected other gases may be used in place of air to enhance the thermal or acoustic insulating properties of the unit. The spacing and sealing system may comprise a spacer frame, commonly lengths of hollow section spacer, for example of aluminium alloy or plastics, joined by right angled corner keys to form a rectangular frame (or a single length of such hollow section spacer bent to form a rectangular with the free ends joined by a key), a primary seal and a secondary seal. The primary seal is composed of a non setting extrudable thermoplastic material with good adhesion to the spacer frame and panes, and a low moisture vapour transmission, such as polyisobutylene, incorporated between the side walls of the spacer frame and the opposing faces of the panes. The primary seal serves to prevent ingress of moisture vapour between the spacer frame and the panes, and may also assist in the assembly of the unit by securing the spacer frame in position between the panes while the secondary sealant is applied and cured. The secondary sealant is usually a two component material which is initially extruded into a channel defined by the outer peripheral face of the spacer frame and the adjacent faces of the opposing panes, but cures in situ to bond the panes and spacer frame together. The secondary sealant, which is typically of polysulphide, polyurethane or silicone, commonly has good adhesive properties and forms a strong bond to both spacer frame and glass; however, the moisture vapour transmissions of the materials used are generally significantly higher than those of the primary sealants. Thus the gas space of the unit may be better protected from moisture ingress (and consequent condensation on the interior surfaces of the panes defining the gas space) by the use of the additional primary seals as described above between the spacer and the panes.
This form of construction is widely used and gives good results. A drying agent, usually of the kind described as a molecular sieve, may be incorporated within the body of the hollow section spacer constituting the spacer frame and be in communication with the gas space between the panes through orifices in the inner peripheral wall of the spacer. This drying agent absorbs any moisture initially present in the gas in the sealed space between the panes, and is also available to absorb further moisture penetrating through or past the primary and secondary seals. Eventually, however, the drying agents become saturated and unable to absorb further moisture so that the moisture content of the gas between the panes increases and water vapour condenses on an internal pane surface; such condensation detracts from the appearance of the unit generally being regarded as amounting to failure of the unit and requiring replacement of the unit.
Typical good quality units have a lifetime of at least 10 years to failure, and many are guaranteed for five or even ten years. There is demand for units with a longer lifetime, but manufacturers are reluctant to offer guarantees as they have been unable to produce units which provide consistently longer lifetimes.
Hitherto, premature failures have generally been associated with poor unit construction, for example, insufficient to poorly mixed secondary sealant, or insufficiently cleaned panes resulting in poor adhesion to the glass, and attempts to provide more reliable and consistent unit lifetimes have generally concentrated on avoiding such construction deficiences.
The present inventors have found, however, and the discovery forms the basis of the present invention, that a consistently long unit lifetime may be achieved for xe2x80x9ctwin sealxe2x80x9d units of the kind described above by using a thicker primary seal than generally used hitherto or recommended by suppliers of the primary sealant material. Thus, for example, one typical sealant supplier recommends the use of 2.5 grams of primary sealant (on each side of the spacer) per meter of spacer frame length, and that the applied primary sealant strip should be compressed to a thickness of between 0.3 and 0.4 mm on assembly of the unit, the corresponding depth of the sealant strip being 4.5 mm. In practice, unit manufacturers tend to use less of the primary sealant material to save cost. Moreover, since the only path for ingress of moisture vapour into the gas space of the unit is between the sides of the spacer and the opposing pane surfaces it has been considered that a wider gap (corresponding to the thickness of the primary sealant) would lead to greater moisture ingress. The inventors have discovered, however, that the use of a sealant thickness greater than 0.4 mm, preferably at least 0.5 mm, enables a consistently longer unit life to be achieved before the dew point is reached and the unit fails, with a much lower risk of premature failure.
Although, as noted above, it has been usual to use a primary seal thickness of less than 0.4 mm, it has been proposed to use a spacer with pre-applied primary sealant on each side to form the spacer frame to avoid the need for applying the primary seal on the double glazing production line, for example the VITROFORM (trade mark) insulated glass profile system. This included a spacer with recesses on the side walls thereof to facilitate pre-application of the primary seal material extending into the recesses: the spacer was designed to be bent in one process into a closed rectangular spacer frame avoiding the need for corner keys as described above, and the width of the primary sealant layer on the sides of the spacer was of the order of 1 mm or more before compression between panes. The thick primary seal, which incorporated a core of circular section of about 1 mm diameter, was used to provide thermal separation between the spacer and the glass unit with xe2x80x9csurface dampingxe2x80x9d for improved sound insulation, but there was no suggestion that its use provided an extended unit lifetime. We have measured the amount of sealant material applied to the sidewalls of the VITROFORM spacer, and found an amount of 6.1 grams (excluding the core) on each side of the spacer per meter of spacer length.
Reverting to the present invention, it will be appreciated that the use of a wider seal than is normal, for a constant seal depth, implies the use of a greater amount of seal material, and in a preferred embodiment of the present invention at least 7 grams of sealant material is used to each side of the spacer frame per meter of spacer length.
According to the present invention, there is provided a sealed insulating unit comprising two parallel opposed panes with a spacing and sealing system therebetween defining, with said panes, a sealed gas space between them, said spacing and sealing system comprising a spacer frame with a primary seal between each side of the spacer frame and the opposing pane face and a secondary seal extending between the panes outside the outer peripheral face of the spacer frame characterised in that each primary seal is greater than 0.4 mm thick on construction of the unit and comprises at least 7 grams of sealant material on each side of the spacer per meter of spacer frame length.
According to a second aspect of the invention, there is provided a method of producing a sealed insulating unit comprising providing a spacer frame of required size, applying primary sealant to each side face of the spacer frame, assembling the spacer frame with and between two opposed parallel panes so that the spacer frame with the panes defines a gas space therebetween and, with a primary seal thickness of greater than 0.4 mm, preferably greater than 0.5 mm, on each side of the spacer frame, applying a secondary sealant into a channel between the panes outside the outer peripheral face of the spacer frame and curing said secondary sealant in situ between the panes. The primary sealant will usually, but not necessarily, be used in an amount of at least 4 grams of sealant material on each side of the spacer frame per meter of spacer frame length.
According to a third aspect of the invention, there is provided the use, in a twin seal sealed insulating unit, of a primary seal between each side of a spacer frame and the adjacent opposing pane having a thickness of greater than 0.4 mm on construction of the unit, to extend the reliable lifetime of the unit. In these second and third aspects of the invention, the amount of primary seal material is preferably, but not necessarily, at least 7 grams on each side of the spacer frame per meter of spacer length.
In each aspect of the invention, each primary seal preferably has a thickness of up to 1 mm on construction of the unit. Each primary seal preferably comprises 7 to 12 grams, especially 9 to 11 grams, of primary sealant material (more may be used but is not cost effective) on each side of the spacer frame per meter of spacer frame length. The opposite sides of the spacer frame facing the panes may be provided with recesses to accommodate at least part of the primary seal material, and ensure that a desired minimum thickness of primary seal material is retained in position when the unit is assembled.
According to a fourth aspect of the invention, there is provided a spacer for a sealed insulating unit comprising two parallel opposed panes with a spacing and sealing system therebetween, the spacer comprising an elongate hollow metal member having opposed outer and inner walls connected together by two opposed side walls, the side walls each defining therein an elongate recess, the dimensions of the recess being selected such that sufficient primary sealant can be accomodated therein to provide in the sealed insulating unit opposed primary seals each at least 0.4 mm thick.
In one preferred embodiment, the recess has an arcuate section having a centre of curvature located laterally within the outward lateral edge of the respective side wall.
In another preferred embodiment, the recess has a section in the form of a trapezium.